Plant-derived secondary metabolites such as taxol or camptothecin are among the most effective chemotherapeutic agents used in cancer treatment. Interestingly, long-lived tree species from various parts of the world have yielded many of the most interesting drug leads. For example, yew trees (Taxus spp.) are the source of the taxanes, a group of structurally unique diterpenes, whereas camptothecin, a quinoline alkaloid, was identified from the bark of the Southeast Asian “Happy tree”, Camptotheca acuminata. 
From a phytochemical point of view, the resin of Guaiacum officinale L. and to a lesser extent Guaiacum sanctum L. has been the subject of many investigations since the early nineteenth century. The resin is purported to contain a number of grouped constituents; resin acids, which are reported to constitute 18-25% of the wood, a number of miscellaneous constituents found in smaller quantities; oils such as guaiol and bulesol, vanillin, terpenes, and quiaicsaponins, and a variety of lignans.
The resin and heartwood of Guaiacum is of particular interest because of its strong association with lignan compounds. Lignans have considerable biological diversity and several have been previously isolated from the heartwood of Guaiacum sanctum L. and Guaiacum officinale L. Guaiaretic acid, dihydroguaiaretic acid, nordihydroguaiaretic acid, guaiacic and α and β guaiaconic acids, have shown some antioxidant activity, with the latter having been reported as a treatment for liver disorders. Furoguaiacidin specifically, has been reported as a 5-lipoxygenase inhibitor and aldose reductase inhibitor and has been successful in the treatment of inflammation, thrombosis, allergies, asthma.
Excluding skin cancer, breast cancer is the most common malignancy among women; accounting for nearly 1 in 3 cancers diagnosed in women (American Cancer Society, 2006). In 2007, an estimated 178,480 new cases of invasive breast cancer were expected to be diagnosed among women and approximately 40,460 women were expected to die from it (American Cancer Society, 2007). The overall breast cancer mortality rate has been declining as a result of awareness, early detection through screening and improved treatment regimens available in the early clinical stages of the disease (NIH, 2003). However, treatment for advanced breast cancer remains at best palliative, with prolongation of survival rather than curative. Survival rates in patients with advanced breast cancer vary with the heterogeneity of the disease, but virtually all will relapse (National Cancer Institute, 2003 and American Cancer Society, 2007). It is evident that cytotoxic therapies for the treatment of advanced breast cancer still remain unsatisfactory. Therefore, the need for new drug development and more effective therapies for advanced breast cancer remain.